Patur aval assur- you said ” No one would use Murex Trunculus as a forgery seeing that it is just as expensive as the actual Techeiles.
Just for the record, Rav Shlomo Miller holds that the Murex Trunculus is in fact Kala Ilan. “”
Why don’t you go ask rabbi miller why someone would use an expensive forgery?
Murex= kla ilan? the aruch is pretty clear otherwise.